Signal processing architecture for modulation and interpolation

Abstract

A system and method for oversampling and modulating a digital data stream. A programmable quadrature interpolating filter is provided which allows the passband of the output signal to be selected from a set of mode selections. The set of mode selections provide overlapping passbands spanning the Nyquist range of the filter. The filter allows a signal to be shifted to a desired carrier frequency before the signal is oversampled and filtered, reducing power consumption in devices such as digital-to-analog converters.

Description

TECHNICAL FIELD [0001] The present invention relates to methods and devices for converting electrical signals from digital to analog format. BACKGROUND [0002] Interpolation and complex modulation are two important functions frequently provided by a signal processing digital-to-analog converter (“DAC”). Interpolation is the process of creating “in-between” samples of a digital signal that are interleaved with the original digital samples (oversampling) and then filtering the output. Filtering removes frequency artifacts from the signal that are introduced by the oversampling. Interpolation increases the sampling rate of the input signal to match the sampling rate of a subsequent signal processing stage. Modulation shifts the center frequency of the digital signal to a desired carrier frequency. [0003]FIG. 1 shows a traditional architecture 100 for implementing these functions. First, interpolation is performed on the components of a complex input data stream 110 by separate real inte...

AI Technical Summary

Benefits of technology

[0004] In an embodiment of the invention, a system is provided for modulating and interpolating a digital data stream. The system includes an input for receiving the digital data stream and a complex modulator for shifting the frequency of the stream to a desired carrier frequency. An interpolator oversamples the frequency shifted stream increasing the clock rate of the system to a desired clock rate. A filter removes undesirable frequency artifacts introduced by the oversampling. In some embodiments of the invention the output of the filter is coupled to a digital-to-analog converter to convert the digital data stream from the filter to an analog output.

Problems solved by technology

A disadvantage of the traditional approach is the need, in general, for a high speed digital local oscillator 150 and modulator 140 to shift the transmission signal frequency to the desired output frequency in the DAC's Nyquist range.

As DAC clock speeds exceed 1 giga-samples-per-second (“GSPS”), the digital oscillator and modulator design becomes increasingly complex and increasing power consumption becomes a concern.

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